There are a lot more barriers to entry now than there were when winning one required a team to go pretty much (but not entirely) undefeated, perhaps convince a bowl's committee to invite you, and convince 35-40 sportswriters they were the best team, which back then mostly required you to go undefeated.
In my lifetime, here are the programs that have won "wow, I can't believe that program won a national title" national titles (emphasis on PROGRAM, not a given team or winning an upset MNC/bowl game):
* Pittsburgh, 1976
* Clemson, 1981
* Miami in 1983
* BYU in 1984
* Colorado and Georgia Tech in 1990
That's it. Any other national title won over that time period, going back into the mid-70s, was won by a program whose name wouldn't have looked out of place against all the other national title winners of that era or earlier--- Alabama, Texas, USC, Ohio State, Oklahoma, Nebraska. Even Michigan or Tennessee, who'd each gone roughly 5 decades between MNCs, were blueblood type programs when they won.
Notice that there aren't any seasons on there since 1990. The Bowl Coalition started with the 1992 season (which is around the time the independents all joined conferences), and the BCS started in 1998, at which time it got really hard for the small-time programs to get invited to the party.
And that's just the invitation. BYU was atop the polls after the regular season in 1984 and all it had to do was beat a 6-5 Michigan team in the Holiday Bowl. In 2021, a G5 team would have to get invited to the playoff and then beat two NFL talent factories like Alabama, Ohio State, Clemson, etc.
I really don't think we'll ever see anything like the 80s again. It is a much more closed system than what existed at that time.